A flash discharge tube, typified by a xenon flash lamp, is widely used as a light source for spectroscopic analysis, a light source for a flash lamp of a camera, a lamp for a high-speed shutter camera or the like because the spectral characteristics of the output light thereof are approximate to sunlight and it can provide stable flash light having a very short light-emission duration. Rare gas such as xenon or the like is filled in such a flash discharge tube. By applying high-voltage pulse current to a trigger electrode disposed in the discharge tube, electrical breakdown is partially induced to form a route through which current flows, and main discharging charges flow from a negative electrode to a positive electrode along this route, so that ionized rare gas induces arc luminescence and light is emitted to the outside. Here, a large current is required to be instantaneously supplied for the main discharge, and thus there is normally adopted such a method that a required amount of electricity is charged in a capacitor for the main discharge in advance, and current is supplied from the main discharging capacitor at the light emission time.